<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>myjQery</title>
    <script src="js/jquery-1.11.3.js"></script>
</head>
<body>
        <li>今天</li>
        <li>明天</li>
        <li>后天</li>
        <li>前天</li>
        <script>
            $('li').css('color','blue').addClass('nav')
        </script>
</body>
</html>